that's Seigmeyer of Catarina. he's the bravest ************ a knight from Dark Souls. his story is tragic. he always tries to be a hero and save everybody, but usually fails, and ends up being rescued by your character, which makes him lose faith in himself, and slowly turns him hollow (feral and hostile). at one point in the game, he offers to sacrifice himself to some deadly creatures so that you may slip away unseen, but if you stay with him and fight, and kill all the creatures, you basically take his last bit of glory away from him, so he starts to hollow. it's a sad story indeed. toward the end of the game, you find out that his daughter has been looking for him, to try and save him and deliver to him the last words of his wife, but by the time she finds him, he is completely hollowed, and she has to kill him.
it's so ******* tearjerking.